1. Field of the Invention
The present invention relates to an exposure apparatus for use in, e.g., a semiconductor lithography process, a stage apparatus suitable for this exposure apparatus, and a device fabrication method.
2. Description of the Related Art
Representative conventional exposure apparatuses for use in the fabrication of semiconductor devices and the like are a step-and-repeat exposure apparatus (also called a stepper) and a step-and-scan exposure apparatus (also called a scanner). The step-and-repeat exposure apparatus moves a substrate (wafer or glass substrate) step by step and sequentially transfers a pattern of an original plate. (reticle or mask) onto a plurality of exposure regions on the substrate by exposure via a projection optical system. The step-and-scan exposure apparatus repeats step movement and scan exposure and thereby repeats exposure transfer onto a plurality of regions on a substrate. In particular, the step-and-scan exposure apparatus uses only a portion of a projection optical system, which is relatively close to the optical axis, by restriction using a slit, and hence can expose fine patterns with high accuracy at a wide field angle. Therefore, this step-and-scan exposure apparatus is expected to be prevalent in the future.
This exposure apparatus has stage apparatuses (a wafer stage and reticle stage) for rapidly moving a wafer and reticle and positioning them. However, driving the stage produces the counterforce of inertia force resulting from acceleration and deceleration. If this counterforce is transmitted to a surface plate, the surface plate shakes or vibrates. Consequently, the natural oscillation of the mechanism of the exposure apparatus is excited to generate high-frequency vibration. This may interfere with high-speed, high-accuracy positioning.
Several proposals have been made to solve this problem of the counterforce. For example, in an apparatus described in Japanese Patent Laid-Open No. 5-77126, the stator of a linear motor for driving a stage is supported by the floor independently of a stage surface plate, thereby preventing shaking of the stage surface plate caused by the counterforce. Also, in an apparatus described in Japanese Patent Laid-Open No. 5-121294, a force actuator for generating force in the horizontal direction with respect to a machine frame supporting a wafer stage and projecting lens applies compensating force equivalent to counterforce produced by driving of the stage. This reduces shaking of the apparatus caused by the counterforce.
In either of the above conventional apparatuses, however, although shaking of the stage apparatus itself can be reduced, the counterforce produced by driving the stage is transmitted to the floor directly or via a member which is regarded as being substantially integrated with the floor. Since this counterforce vibrates the floor, apparatuses arranged around the exposure apparatus may be given vibrations and adversely affected. Generally, the floor on which the exposure apparatus is installed has a natural frequency of about 20 to 40 Hz. Therefore, if this natural frequency of the floor is excited by the operation of the exposure apparatus, the adverse effect on the peripheral apparatuses is enormous.
Recently, the stage acceleration is increasing steadily with the improvement of the processing speed (throughput). For example, the maximum stage acceleration of the step-and-scan exposure apparatus is 4 G for a reticle stage and 1 G for a wafer stage. Additionally, the stage mass is also increasing with the increase in size of a reticle and substrate. Accordingly, the driving force defined by  less than mass of moving body greater than xc3x97 less than acceleration greater than  becomes very large, and its counterforce is very large. Hence, the vibration of the installation floor caused by the acceleration increase and weight increase is a problem to be solved.
The present invention has been made to solve the above problem, and has as its object to provide an exposure apparatus obtained by further advancing the above conventional apparatuses.
It is another object of the present invention to provide an exposure apparatus capable of particularly reducing the influence of vibration or shaking caused by the movement of a wafer stage and achieving higher accuracy than in the conventional apparatuses, and also improving the throughput.
It is still another object of the present invention to provide an exposure apparatus capable of reducing the influence of the counterforce produced by the acceleration and deceleration of a wafer stage on the floor, and thereby reducing the influence on other apparatuses installed on the same floor.
It is still another object of the present invention to provide a device fabrication method using the above exposure apparatus and having high productivity.
One form of the exposure apparatus of the present invention which solves the above conventional problem is an exposure apparatus comprising a reticle stage for holding a reticle, a wafer stage for holding a wafer, and a projection optical system for projecting a pattern of the reticle onto the wafer. This exposure apparatus performs exposure by scanning both the reticle stage and the wafer stage with respect to the projection optical system, and transfers the reticle pattern onto a plurality of shot regions on the wafer in order. The apparatus is characterized in that the plurality of shot regions arranged along a scanning direction on the wafer are intermittently exposed by moving the wafer stage by scanning without stopping it.
Preferably, the shot regions arranged in the scanning direction are exposed by scanning in order while one or more shot regions are skipped without being exposed. Preferably, the reticle stage is moved in the opposite direction to the direction of scanning during the skip period. Preferably, the skipped shot regions are similarly exposed later while the exposed shot regions are skipped.
Preferably, the velocity of the wafer stage is held constant during the scan exposure and the skip period, or, the velocity of the wafer stage during the skip period is changed from that during the scan exposure.
Preferably, alignment measurement or focus measurement is performed during the skip period. The measurement result is reflected on exposure of the next shot or an adjacent shot. Alternatively, the apparatus includes a means for storing the measurement result, and the measurement result is reflected when the skipped shot regions are exposed later. Also, alignment is performed for each shot by a die-by-die mode, or this position information of each shot is added to position information of the shot previously obtained by global alignment.
Preferably, multiple exposure is performed for each shot region by using a plurality of wafers. For example, this multiple exposure is performed by using a first reticle for transferring a line-and-space periodic pattern and a second reticle for transferring an isolated pattern. For example, after the first reticle is exposed, the interval to exposure of the second reticle is held substantially constant for all shot regions. For example, the line-and-space pattern is exposed by the first reticle by moving the wafer stage while the reticle stage is stopped.
Another form of the exposure apparatus of the present invention is a scanning exposure apparatus for performing multiple exposure of first and second patterns. This exposure apparatus is characterized in that scan exposure is performed by moving a wafer stage while a reticle stage is stopped during the exposure of the first pattern, and scan exposure is performed by moving both the reticle stage and the wafer stage during the exposure of the second pattern.
Preferably, the apparatus includes a mechanism for reducing the influence of counterforce produced when the wafer stage or the reticle stage is driven. This mechanism is constructed of a stage base member for supporting the wafer stage, and a counterforce receiving structure, different from the stage base member, for receiving the counterforce produced when the stage is driven. Transmission of vibrations having a predetermined frequency or more is interrupted between the counterforce receiving structure and the floor.
The device fabrication method of the present invention is characterized by fabricating devices by fabrication steps including the step of preparing any of the abovementioned exposure apparatuses and the step of performing exposure by using the exposure apparatus.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.